The present invention relates to a surgical instrument, and in particular to a surgical instrument including an intramedullary rod.
Intramedullary rods can be used in knee arthroplasty procedures to provide a reference to which a cutting guide or block can be attached for performing a femoral cut. It will be appreciated that the present invention relates to intramedullary rods which provide a reference or some other feature or component which is used during preparation of the bone rather than to the type of rods which are placed inside the intramedullary canal to and secured with bone screws or similar as used to repair broken bones or in other trauma type applications.
Intramedullary rods typically are of order 40 cm or so long from the tip of the rod to the bone engaging formation which engages the bone surface in use. The end of the rods of such length become fixed in the intramedullary canal and so are self locating. However, the intramedullary canal varies from patient to patient in terms of its width, direction and straightness and so the intramedullary rod position can be compromised when using such long rods. Hence, the positioning of components attached to the rod, such as a cutting block, can also be compromised, and it can be difficult if at all possible to correctly position the cutting block.
It can be desirable to provide some angular adjustment so that the angular orientation of the cutting guide or block can be changed either to compensate for patient anatomy or otherwise to allow the femoral cut to be made at a preferred angle.
Intramedullary rods which allow angular adjustment exist, but they can be difficult to use in practice. FIG. 1 shows an existing assembly 10 including an intramedullary rod 12 which is pivotably attached to a body by a pivot mechanism 14 which can be operated by a user to selectively change the angle of the rod, for example, by operating a lever 16 to engage/disengage teeth to allow the rod to freely pivot. Hence the angle of the rod 12 can be adjusted relative to a cutting block 18. However, such prior pivoting mechanisms can be difficult to use in practice. The lever to be operated is often small and difficult to operate with the rod 12 inserted into the femur 20. Also, because of the construction of the pivot mechanism, very little space can be available for the different selectable angles and so it can be hard to ensure that the correct angle is selected. Furthermore, there can be very little space available on which to display any scale so that the user can either see or check the angle that they want.
Therefore, it would be desirable to provide an intramedullary rod with angular adjustment which can be used more easily and/or which can be located in the intramedullary canal more easily.
The present invention provides a femoral instrument including a short intramedullary rod with a centraliser mechanism so that the short rod can be self centralised in the intramedullary canal allowing the rod and other components attached to the rod to be more easily positioned relative to the bone in use.
The present invention also provides a femoral instrument including an intramedullary rod with an angular adjustment mechanism adapted to make the instrument easier to use in terms of its operation and reading of its scale.